This invention relates generally to pneumatic tires for motor vehicles and in particular to tires for passenger cars.
Vehicle tires having treads comprising a plurality of block elements are well known. It is further known that in tires for high speed passenger cars the treads may comprise a plurality of block elements arranged in axially spaced apart circumferential rows.
It is also known to form tire treads with circumferential ribs which are each divided into short sections by cross-lits. If the cross-slits are oriented at an acute angle relative to the mid-circumferential plane of the tire, then adjacent parts of the rib can move relative to each other resulting in a tire which exhibits good handling performance, reasonable traction, and good wear properties. Such a tire is illustrated in GB-A-2 051 694 which teaches a tire primarily for use as a truck tire in a steering position.
There is disclosed herein a particular structure for tires having treads comprising circumferential ribs divided into short sections by cross-slits, which can be adapted for use as high performance tires, i.e. tires that can be used on passenger cars that are capable of running at speeds in excess of 190 km/hour (115 miles/hour).
There is provided in accordance with one aspect of the invention, a pneumatic tire comprising a ground contacting tread having a plurality of grooves extending circumferentially thereabout and two series of decoupling sipes which cooperate with one another to divide the tread into axially spaced apart lands, each of said lands being subdivided into a plurality of four-sided blocks by a series of cross-slits that extend across the respective lands, the cross-slits in each land being arranged to circumferentially alternate between first cross-slits extending in substantially axial directions and second cross-slits extending in directions which are inclined at acute angles with respect to the mid-circumferential plane of the tire, each of the cross-slits having a centerline that is a straight line and the blocks in each land being arranged such that circumferentially adjacent blocks are axially offset relative to each other thereby forming in the walls of the circumferential grooves a series of spaced notches.
The cross-slits may be in the form of sipes or blades, or may alternatively be a mixture of sipes and grooves. By "sipes" or "blades" are meant cross-slits which close up in the footprint of the tire and by "grooves" are meant cross-slits which do not close up in the footprint of the tire when the tire is mounted upon its specified rim, inflated to its recommended inflation pressure, and subjected to its rated load for said inflation pressure. It is understood for the purposes of the present invention that the specified rim, inflation and load for a tire may be determined either by the tire manufacturer's specifications as molded into a sidewall of a tire, or by the specifications published for a tire of a given size and ply/load rating as set forth in either the yearbook of The Tire and Rim Association, Inc. or the European Tyre and Rim Technical Organization for the year in which a tire is manufactured.
The terms "radial" and "radially" refer to planes which contain the axis of rotation of a tire, the terms "circumferential" and "circumferentially" refer to the direction of rotation of a tire, and the terms "axial" and "axially" refer to displacements parallel to the axis of rotation of a tire. The term "substantially axially" refers to directions that do not vary by more than 5.degree. from being parallel to the axis of rotation of a tire.
The mid-circumferential plane of a tire is a plane which is perpendicular to the axis of rotation of the tire and which is located midway between the lateral edges of the tread in a footprint of the tire when the tire is mounted upon its specified rim, inflated to its recommended inflation pressure and subjected to its rated load for said inflation pressure.